The invention relates to phosphoric acid fuel cells and more particularly to a dry compliant overlapping peripheral seal for such cells.
Phosphoric Acid Fuel Cells provides an environment for an electrochemical reaction between a fuel and oxidant to create electrical energy. Each fuel cell comprises an anode and a cathode assembly with a matrix disposed therebetween. While the cells may be any shape they, are normally rectangular and stacked one on top of another forming a stack of fuel cells with manifolds disposed on opposite sides of the stack for supplying fuel and oxygen to the cells and for removing spent gases from the cells. The cells are disposed between bipolar plates made of graphite with a plurality of grooves on opposite sides thereof to either supply fuel, such as hydrogen, to the anode and oxidant such as oxygen to the cathode. The anode assembly is formed by providing a layer of catalyst on a graphite backing paper. The cathode assembly is also formed by providing a catalytic layer on graphite backing paper. Between the catalytic layers of the anode and the cathode is a porous graphite layer and a silicon carbide layer, which together form the matrix. The silicon carbide layer acts as an insulator to prevent electrons from traveling from the anode assembly to the cathode assembly of the same fuel cell, thus causing an electrical short circuit. Portions of both anode and cathode assemblies and the entire matrix assembly are sufficiently porous and hydrophilic to allow the electrolyte, phosphoric acid, to permeate therethrough. The high temperature of the anode gas in the presence of the catalyst results in the ionization of the hydrogen and the release of electrons. The hydrogen ions diffuse through the electrolyte and react with the oxygen and free electrons in the catalytic layer of the cathode in the same cell. The electrons, freed from the hydrogen, flow through the conductive bipolar plate to the cathode in the next cell or to the external circuit in the case of the end cell. The end cells of the stack of cells provide the electrons for the load current connecting the anode of one end cell to the cathode of the other end cell.
U.S. Pat. No. 4,374,185 describes a stack of phosphoric acid fuel cells having irregular edges, which engage a flange surrounding pan shaped gas manifolds that incorporates seals made of Polytetrafluoroethylene, a material sufficiently compliant to compensate for the irregular edges on the faces of the stack of fuel cells to form a gas tight seal.